CC(Cl)(Cl)Cl (b) O=[N+]([O-]… # Which of the following is obtained when 4-chlorobenzene sulphonic acid is treated with excess sodium acetate? (a) N#CC(Cl)(Cl)Cl (b) O=[N+]([O-])c1ccc(Cl)cc1 \(+\mathrm{CH}_{3} \mathrm{COOH}\) COC(=O)c1ccc(O)cc1 \(\mathrm{NaOH}\) (c) O=C(O)Cc1ccc(Cl)cc1 (d)

Write out the structure of 4-chlorobenzene sulphonic acid and sodium acetate. 4-chlorobenzene sulphonic acid: c1ccc(Cl)cc1S(=O)(=O)OH Sodium acetate: \(\mathrm{CH}_{3} \mathrm{COONa}\)

We have a reaction between an aromatic sulphonated compound and a carboxylate ion. This type of reaction is known as electrophilic aromatic substitution (EAS), where an electrophile will attack the aromatic ring and replace a group already present.

Now we will look at the possible products given and determine which one should be formed by analyzing the electrophilic aromatic substitution taking place. (a) N#CC(Cl)(Cl)Cl This product does not include the aromatic ring present in the reactant and looks unrelated to the reaction. (b) O=[N+]([O-])c1ccc(Cl)cc1 \(+\mathrm{CH}_{3} \mathrm{COOH}\) This product represents a nitration reaction, which is not expected in the reaction with sodium acetate. (c) O=C(O)Cc1ccc(Cl)cc1 This product represents an electrophilic aromatic substitution, with the sulphonate group replaced by an acetyl group. This product is expected when the reaction takes place with sodium acetate. (d) COC(=O)c1ccc(O)cc1 This product would represent a hydroxylation of the aromatic ring, which is not expected with sodium acetate.

Based on the analysis of the reactants and possible products, the product obtained when 4-chlorobenzene sulphonic acid is treated with excess sodium acetate is choice (c): O=C(O)Cc1ccc(Cl)cc1.